The invention relates to improvements in apparatus for treating running webs of photosensitive material, such as exposed but undeveloped photographic films or strips of photographic paper. More particularly, the invention relates to improvements in apparatus for wet treatment of running webs of photosensitive material. Still more particularly, the invention relates to improvements in apparatus of the type disclosed in commonly owned U.S. Pat. No. 4,967,222 granted Oct. 30, 1990 to Wilhelm Nitsch for "Method of and machines for treating webs of photographic material". The disclosure of this patent is incorporated herein by reference.
Large photographic processing laboratories, wherein exposed customer films are developed and selected developed film frames are imaged on photographic paper, tend to utilize entire production lines in an effort to reduce the number of attendants and to speed up the developing, copying and printing operations. A modern production line is designed in such a way that neither the films nor the photographic paper must be stored at any location between the inlet for cartridges or cassettes which contain customer films and the outlet for sections of exposed and developed customer films and the corresponding prints on exposed and developed photographic paper. Thus, when such processing laboratories, known as maxilabs, receive cassettes of customer film, an attendant at the inlet of a production line inserts successive cassettes into a dark chamber and the cassettes are automatically relieved of exposed films, the films are spliced together end-to-end into a long web of coherent films, the web is caused to pass through a developing machine, the developed web is caused to pass through a copying machine wherein selected film frames are imaged onto photographic paper, the paper is thereupon developed, and the thus obtained prints are separated from each other and gathered with the associated film sections to be withdrawn by an attendant at the outlet of the production line. Such attendant inserts the prints and the associated customer films into envelopes which are picked up or shipped to dealers or directly to customers. All this is fully described and illustrated in the patent to Nitsch. It has been found that the output of a production line of the above outlined character is much higher than the output of a series of discrete machines which are in use in many conventional photographic processing laboratories. Of course, a prerequisite for proper functioning of a production line is that the operation of each of its constituents (such as discrete splicing, developing, copying, severing and other units) is properly synchronized with the operation of each other constituent. Serious problems are encountered in connection with the synchronization of operation of the developing unit for photographic paper with the operation of the preceding and following units. The reason is that, in order to obtain sharp reproductions of images of selected exposed and developed film frames, photographic paper must be maintained in each bath of the developing unit for an accurately determined interval of time.
Nitsch discloses a method and an apparatus for selecting the length of the path for a web of photo-sensitive material through a liquid bath as a function of the speed of the web so that the interval of contact between the body of liquid and each film frame or each unit length of photographic paper remains unchanged even if the speed of the web varies within a wide range. The patented apparatus employs tanks with sets of upper and lower pulleys, and the webs are trained alternatingly over the upper and lower pulleys so that they advance along meandering paths. The upper pulleys are rotatable about fixed axes and the lower pulleys are mounted on a common carrier or support which is guided in the respective tank for movement toward and away from the upper pulleys. Thus, the length of the path for a running web through a particular liquid bath can be increased or reduced by the simple expedient of moving the lower pulleys away from or toward the respective upper pulleys. The common carrier or support for the lower pulleys can be moved up and down by a motor in dependency on the momentary speed of the web in the respective tank. A web drive at the discharge end of the tank cooperates with the drive for the vertically movable carrier or support in order to ensure that the speed of withdrawal of successive increments of the web is properly synchronized with the movements of the lower pulleys toward or away from the upper pulleys and to thus ensure that the period of dwell of each increment of a web in the respective body of liquid matches an optimal interval of time. The just described controls of Nitsch are reliable but rather complex and expensive.
Furthermore, it has been found that friction between the liquid in a developing or other tank and the running web of photosensitive material, especially photographic paper, rises considerably when the web is transported at a presently required speed of approximately 50 meters per minute. Such friction causes the development of a pronounced tensional stress in the material of the web, and the tensional stress rises as a result of training of the web upon a series of pulleys, sheaves or like web guiding or deflecting members. In fact, the tension in a web which has been trained over five pulleys can reach a value at which the web tears to thereby cause lengthy interruptions in the operation of the entire production line. Proposals to avoid such undue tensional stressing of the web include the provision of relatively small web guiding and advancing assemblies each of which employs a small number of upper and lower pulleys (so that the total number of deflections of a web which is being advanced by one of these assemblies is not more than five), a carrier for the lower pulleys, a drive at the outlet end of the assembly and a drive for the carrier. Each tank of the developing unit employs two or more assemblies of the above outlined character, and the breaking up of the apparatus of Nitsch into two or more assemblies is carried out for the sole purpose of avoiding tearing of the web in a body of developing, fixing, rinsing or other liquid. It is clear that the utilization of two or more web advancing and guiding assemblies in each tank of a developing machine for photographic paper or other photosensitive material contributes significantly to the cost of the production line.